1. Field of the Invention
The present invention relates to an image pickup apparatus capable of shooting at high frame rate, a control method therefor, and a computer-readable storage medium storing a control program for implementing the control method, and in particular to a technique of suppressing image degradation, which results from camera shake, using images taken at high frame rate.
2. Description of the Related Art
In general, some image pickup apparatuses such as digital cameras align a plurality of images in a plurality of frames and then synthesize the images so as to suppress image degradation resulting from camera shake. Here, frames may refer to not only frames for moving images but also respective ones of a plurality of still images when the plurality of still images are taken using a so-called continuous shooting function.
The alignment mentioned above is carried out so as to reduce the effect of image blurring caused by movement of a subject (so-called motion blur), and for example, a moving vector (motion vector) between temporally-adjacent frames is obtained. This moving vector represents a difference in the position of a subject or the like between the frames. Based on the moving vector, a plurality of images are aligned (registration process), and thereafter, the plurality of images are synthesized.
It should be noted that in the registration process, the images are aligned within a search range determined in advance.
On the other hand, there has been a method that obtains moving vectors between frames, which are not temporally adjacent to each other, so as to reduce computation loads and stabilize an image (see Japanese Laid-Open Patent Application (Kokai) No. 2007-214666). Here, a moving vector between the oldest frame and the newest frame among a plurality of frames stored in memory is computed.
Further, there has been a method that, in order to reduce computation loads required to detect a moving vector, determines a search range for use in obtaining a moving vector between the Nth frame and the (N+1)th frame based on a moving vector obtained using the (N−1) frame and the Nth frame (see Japanese Laid-Open Patent Application (Kokai) No. 2007-267232).
However, according to the methods described in Japanese Laid-Open Patent Application (Kokai) Nos. 2007-214666 and 2007-267232, if the number of images to be synthesized increases due to a rise in frame rate, the amount of computations (processing time) therefor will remarkably increase with frame rate. The increase in processing time brings about degradation in convenience for a user.